Along with other demands made of an ideal injection behavior is the demand for independent definition of the injection pressure and injection quantity, which should both be freely selectable for any operating point in which an internal combustion engine can be operated. This provides one additional degree of freedom in terms of the mixture formation. In addition, at the onset of injection the injection quantity should be as slight as possible, to compensate for the resultant ignition lag between the onset of injection and the onset of combustion. Both demands are met by fuel injection systems with a high-pressure collection chamber (common rail), by way of which the individual injectors are supplied with fuel that is at extremely high pressure for the combustion chambers of the engine.
European Patent Disclosure EP 0 657 642 A2 relates to a fuel injection system for internal combustion engines. It includes a high-pressure collection chamber, which can be filled by a high-pressure pump and from which high-pressure lines lead away to the individual injection valves. In the individual high-pressure lines, control valves are provided for controlling the high-pressure injection at the injection valves, along with an additional pressure reservoir between these control valves and the high-pressure collection chamber (common rail). To prevent the high system pressure here from being applied constantly to the injection valves, the control valve is embodied such that during the intervals between injections, it closes its communication at the injection valve with the pressure reservoir and opens a communication between the injection valve and a relief chamber.
From U.S. Pat. No. 5,628,293, an electronically controlled fluid injector is known, with which a fluid collection chamber that can be acted upon by a preinjection and with directly triggerable control elements to open the connecting line between the fluid collection chamber and the injection nozzle that protrudes into the combustion chamber of an internal combustion engine. Besides the first, directly triggerable injection element, a further pressure control element is movable back and forth between two control positions. By means of the two switchable pressure control elements, hydraulic forces acting counter to one another can be balanced. In this configuration, the fact that controlling the pressure elements is done via two units, which when the control device is selected are secured only partly against a resultant overpressure or a resultant excess quantity of fuel, is a disadvantage.
With the injector configuration according to the invention, an opening that takes place in preselectable stages and a graduated closure of the nozzle needle of an injector are brought about. To attain a main injection into the combustion chamber of a direct-injection internal combustion engine, and to perform a postinjection into the combustion chamber, the injector needs to be triggered only a single time, which in terms of the electrical power means a 50% savings in electrical energy. Along with a 50% savings of electrical energy for triggering the injector, the switching forces can be minimized by choosing the same diameter for the guide diameter and the seat diameter, since in that case the valve body is force-balanced.
By the design of the throttles on the outlet and inlet sides of the control chamber for a nozzle needle, the injector can be properly designed. If a parallel change in both throttle restrictions takes place, the fuel volume throughput remains the same upon adaptation of the control valve. With the proposal according to the invention, a pressure-controlled injector is created whose valve chamber, surrounding the valve body, communicates with a control chamber that can act upon the nozzle needle. At the same time, this control chamber communicates on the inlet side with the supply to the nozzle chamber via a throttle element. This configuration opens up the possibility, by partial pressure relief of the control chamber acting on the nozzle needle, of moving the nozzle needle in graduated fashion, that is, to impose partial stroke lengths on it, so that an optimal injection characteristic, for instance for utility vehicle engines, can be attained.
Along with the possibility of establishing a graduated vertical motion and thus an injection characteristic that is especially well suited to applications in utility vehicles, the proposed pressure-/stroke-controlled injector is especially simple in construction and therefore can be produced economically.